AGRICULTURE

Farmers' dependence on the weedkiller Roundup and its generic alternatives threatens to undermine environmental gains that have accompanied widespread use of genetically engineered crops, the National Academy of Sciences said in a report today.

More than 80 percent of the corn, soy and cotton grown in the United States has been engineered with bacterial genes to resist insect pests or the Roundup herbicide, also known as glyphosate. The glyphosate-resistance trait has become so prevalent that many farmers now have a "nearly exclusive reliance on glyphosate for weed control," the report says.

Since the introduction of glyphosate-resistant crops, up to nine important weed species, like giant ragweed and pigweed, have independently evolved resistance to the weedkiller. This resistance was not spread by the crops' pollen, but rather through strong selection pressure caused by the nearly indiscriminate use of the herbicide.

"We've got a significant weed-resistance problem," said David Ervin, the report's lead author and a professor of environmental management and economics at Portland State University. "That's an issue that's not going to go away. And it has to be dealt with, as it could jeopardize the usefulness of the technology down the road."

Once resistance has appeared in a weed, farmers often revert to old habits. They ramp up glyphosate use and add other, more toxic herbicides into the mix, mitigating the environmental gains found in using only glyphosate, which does little harm to animals or soil. Tillage also tends to increase, decreasing soil quality.

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To maintain the value of the technology, farmers must employ more diverse weed-management practices, which include rotating herbicides and application methods, and better mechanical control practices. Though large commercial farms have long known about such methods, they have been loath to implement them, the report says.

"Although the strategies to mitigate weed shifts are readily identified," the report says, "they have largely been ignored because of the scale of commercial agriculture, which favors the simplicity, convenience and short-term success of herbicide use over more time-consuming strategies that can be burdensome to implement on farms."

The seed giant Monsanto Co. originally developed glyphosate and has introduced the genes necessary for resistance in corn, soy and cotton. The firm may have less incentive to stop the spread of weed resistance than in the past, however, as the company's patent on glyphosate expired in 2000. Since then, generic Roundup options have flooded the market.

The report also found that the public cannot expect corporations like Monsanto and its prime competitor, DuPont, to modify minor crops like fruits and vegetables, from which little money is to be made. Government, which has long seen its investments in crop breeding decline, should reinvest in this area and spur public-private partnerships that would develop crop traits beneficial to the public, such as improved nutrient absorption or added vitamin expression.

"We can't count on the industry to do that in full," Ervin said. "We endorse a strong program of public-funded research."

The government should take steps to overhaul and streamline its regulatory apparatus for modified crops, the report says; Congress has never passed a law regulating the industry. And more steps should be taken to examine and deal with the ramifications of gene flow, the spread of pollen and engineered genes from modified crops into organic varieties (Greenwire, Oct. 8, 2009).

In the end, the study -- the first comprehensive look the academy has taken on the effect of GM crops on sustainable farming -- was unable to make conclusions on a variety of topics due to a frustrating lack of data, Ervin said.

"There's some pretty important holes that need to be filled," he said.

Studies of the economic impact of the crops, including the gains from glyphosate and drawbacks of spiraling seed prices, tailed off earlier this decade. And while advocates of GM crops say they have been beneficial to water quality, scant evidence qualifies this claim, Ervin said.

The social impact of GM crops has also been sorely neglected. The scientists on the study would hear anecdotes about farmers being unable to purchase unmodified seeds or strife between organic and GM farms, but little peer-reviewed research backs these stories. And while some studies have been done on the effects of consolidation in the seed industry, not nearly enough research is happening, Ervin said.